P20140723; July 23, 2014

³Measured position corresponds to RA offset of –0.1950'' and Dec. offset of –0.0495''.

⁴All "offsets" are defined in the ("corrected" – "reference") or ("observed" – "calculated") sense. The offsets should be added to reference positions to get the measured positions, which we use to calculate the prediction.

⁴Data analyzed using UCAC2 reference network. A weighted average of the data from the two telescopes was used to calculate the RA and DEC. The errors given are 1 standard deviation.

⁵The reference positions for Pluto and Charon and Nix are those given by JPL Horizon's ephemeris (Nix source file: PLU043; Earth center source file: DE431). Our residual model is based on the assumption that the same offsets in RA and Dec apply to both Pluto, Charon, and Nix.

⁶Data from the USNO 61-inch, Lowell 42-inch telescope, SARA-South 24-inch telescope, and Lowell Astrograph telescopes over the span of 5 years were reduced with respect to stars in the UCAC2 catalog. A model was developed to fit the residuals obtained from our measured positions compared to that of the object's JPL ephemeris. All residuals obtained from the different telescopes were consistent with the model. The model includes the first-order effects of errors in the orbital elements of Pluto: (i) constant offsets in RA and Dec, (ii) linear (in time) offsets in RA and Dec, (iii) sinusoidal terms with the Earth's orbital period, and (iv) sinusoidal terms with the Pluto-Charon mutual orbit. The model was propagated to obtain the predicted position and error of the Pluto at the time of the occultation. The errors listed for the Pluto are the RMS of the models fitted.

Table 1: Prediction Details
Pluto Geocentric Mid-time (yyyy month dd hh:mm:ss)	2014 July 23 06:35:06± 00:00:42¹ UT
Pluto Minimum Geocentric Separation	0.144± 0.040¹ arcsec
Position Angle (Pluto relative to the star; measured north through east)	169.89 degrees
Geocentric Velocity	22.44 km/sec
Occultation Star UCAC2 magnitude	14.98²

Table 2: Reference Star Position
Reference star position: (UCAC2, at epoch of event)	RA (h:m:s; J2000)	Dec (d:m:s; J2000)	Notes
N20140723 Catalog	18 49 33.6250± 0.2049	–20 22 16.941± 0.198
N20140723 Measured³	18 49 33.5994± 0.0139	–20 22 17.068± 0.007	USNO 61-inch Telescope frames. See note 4.
Table 3: Projected KBO Offsets from Reference Ephemeris at the Time of the Event
Body	RA (arcsec)	Dec (arcsec)
Pluto	+0.0207± 0.0381	+0.029± 0.040	See Notes 5 and 6
³Measured position corresponds to RA offset of –0.1950'' and Dec. offset of –0.0495''. ⁴All "offsets" are defined in the ("corrected" – "reference") or ("observed" – "calculated") sense. The offsets should be added to reference positions to get the measured positions, which we use to calculate the prediction. ⁴Data analyzed using UCAC2 reference network. A weighted average of the data from the two telescopes was used to calculate the RA and DEC. The errors given are 1 standard deviation. ⁵The reference positions for Pluto and Charon and Nix are those given by JPL Horizon's ephemeris (Nix source file: PLU043; Earth center source file: DE431). Our residual model is based on the assumption that the same offsets in RA and Dec apply to both Pluto, Charon, and Nix. ⁶Data from the USNO 61-inch, Lowell 42-inch telescope, SARA-South 24-inch telescope, and Lowell Astrograph telescopes over the span of 5 years were reduced with respect to stars in the UCAC2 catalog. A model was developed to fit the residuals obtained from our measured positions compared to that of the object's JPL ephemeris. All residuals obtained from the different telescopes were consistent with the model. The model includes the first-order effects of errors in the orbital elements of Pluto: (i) constant offsets in RA and Dec, (ii) linear (in time) offsets in RA and Dec, (iii) sinusoidal terms with the Earth's orbital period, and (iv) sinusoidal terms with the Pluto-Charon mutual orbit. The model was propagated to obtain the predicted position and error of the Pluto at the time of the occultation. The errors listed for the Pluto are the RMS of the models fitted.

Site	East Longitude	Latitude	Site Altitude⁶ (km)	Nix Distance⁷ (km)	Velocity (km/s)
Cerro Calan	–70 32 48	–33 23 48	0.86	683 N.	22.67
DCT	–111 25 18	+34 44 41	2.337	8346 N.	22.81
Mt. John	170 27 50	–43 59 22	1.041	502 N.	22.57
Geocenter	----------	---------	center of Earth	3308 N.	22.44

Site	Nix Immersion (UT)⁹	Nix Mid-Time (UT)	Nix Emersion (UT)⁹	Nix Altitude	Solar Altitude⁹
Cerro Calan	-----------	06:32:34	-----------	47	-----------
DCT	-----------	06:34:05	-----------	34	-----------
Mt. John	-----------	06:38:45	-----------	27	–12
Geocenter	-----------	06:35:06	-----------	-----------	-----------

N20140723 Occultation July 23, 2014